Acoustic imaging in enclosed spaces: Analysis of room geometry modifications on the impulse response

Abstract

Sound propagation in enclosed spaces is characterized by reflections at the boundaries of the enclosure. Reflections can be wanted in the case when they support the direct sound or give a feeling of envelopment or they can be unwanted when they lead to echoes and colouration. When measuring multiple impulse responses in an enclosed space along an array the reflections can be mapped to the reflecting objects. Similar to seismic exploration, medical diagnostics, and underwater acoustics, an image of the reflecting objects is obtained in terms of reflected energy. The imaging process is based on inverse wave field extrapolation with the Kirchhoff–Helmholtz and Rayleigh integrals. The inverse of the imaging process recreates the measured impulse responses from the image and it allows one to remove or alter reflecting objects in the image and investigate their influence on the wave field in the enclosed space in a physically correct way. This can be verified by reimaging the altered wave field. Preliminary results from listening tests for the perceptual evaluation are presented. They indicate that the influence of a reflecting object can only be perceived in its close proximity.

Estimation of reflective surfaces from continuous signals

“…Kuster uses acoustic imaging for finding the room geometry and other acoustic properties [5,6]. Acoustic imaging is similar to the methods used in underwater acoustics.…”

“…The problem of room geometry estimation using microphones and loudspeakers has been addressed by several authors with various approaches [3,4,5,6]. All of the previously introduced methods use a prior knowledge of the source signal.…”

“…It is based on the inverse extrapolation of the Kirchoff-Helmholtz and Rayleigh integrals. An acoustic image of a room is constructed by measuring multiple impulse responses for example on a line grid with B-format microphone [5,6].…”

Reducing time in acoustic impulse response measurements using exponential sine sweeps

“…When attempting to characterize the maximum of acoustic sound field information for an acoustic room or hall, usually a huge number of impulse response measurements are employed [4] [5]. This could easily lead to hours of test signal playing without considering the time of equipment positioning and signal processing of the data collected.…”

Localization of distinct reflections in rooms using spherical microphone array eigenbeam processing

“…7 More recently, the deployment of microphone arrays allows one to extract further spatial information about the acoustic environment, including early reflection localization from the measured spatial room impulse responses. [8][9][10][11] For full three-dimensional (3D) scene analysis, a spherical array can be applied to sample the wave field. [12][13][14] In particular, signal processing can then be performed using the spherical harmonics [eigenbeams (EB)] for acoustic wave field representation.…”